ML20059D006
| ML20059D006 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 08/21/1993 |
| From: | AFFILIATION NOT ASSIGNED |
| To: | |
| References | |
| OLA-2-I-MFP-128, NUDOCS 9401060314 | |
| Download: ML20059D006 (19) | |
Text
O~27 323-00 26-Is (3/st) qAP-15.3 f__ /lg jr[) - / 2.@
NMbD y Q 10/24/90 2/ M NoncowroRMANCE REPORT 4 i toi 12/31/90 t
thseber Rev.
2.
Qality Probles Report No. (if applicable) 1.
NCR Hant Vaar Depu.
N_.Q?.,5 /
A0267535 No.
Dr' 09 -
6.
M orence 3 d
? Nd 3.
Ites/ Activity Valve Failed to F.311v nnen 5.
Description of konconformances j
SI-2-8923A. Valve, will not stroke fully open, subsecuent investication revealed j
that the worm cartridee bearinc locknut setscrew had backed off/ loosened F r n the I
worm shaft preventine the valve from fully openine.
This is considered a f
nonconformance ner AAP 1%.k.
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- 10. Ortanization
- 11. Date C,
7 Organization
- 3. Date llect. Maint.
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- 12. NCHEvaluationAttachedontheNCRTextContinuationSheetMl h
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Plant Conditions III. Cause of Problee V.
Corrective Actions 4
A II. i=scrlption of Probles
!Y.
Analysis of Problem VI. Additional Information L
1 7
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- 16. Eatinated
- 15. Responsible E
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- 13. Trend Other Completion Organization C
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[ hl-lAl6l ll-lll l l-l l l Date H
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16.
10CFRSO.73
- 17. Potentially 10CTR21
- 18. 1DCTR$0.9
- 19. Reference Other C
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A P
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Yes l j No l)0 Yes ll No IX)
INP0 Network L
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- 20. nasts Refer to Attached A
Initial
- 21. Time Limit
- 22. Method
- 23. Notified By
- 26. Time
- 25. Date 8
8 8'Por' N/A N/A N/A N/A N/A E
I v
L Followup
- 26. Requir1Hi
- 27. Time Limit
,23. In No.
- 29. Date 1
1 Report Yes l )
No l 4 N/A N/A N/A E
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- 30. Other Agencies Notified None it.
Remarks 1
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Chairman (p/s 33.
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Date NSKoe is 9 /
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- 39. Dat
- 66. Other (p/s) 67.
Date PSRC
=B. / Meeting Date 49 GOhfkAC Nottiacatnon Dates R.2 view -
Corrective
- 50. Comp l e te - TRG Qiairman (p/s)
- 51. Date
- 52. QA verification by (p/s)
- 53. Date Action P
9401060314 930821 PDR ADDCK 05000275
.. Lij s t ri tm t i c" G
PDR NPC
/
Manager,<QA
. Materials PSRC Secreta'ry Station / Hydro Construction Initiator Plant Manager, DCPP TES Appropriate QC CONPRAC Secretary Authorised Inspector, Other
, Engineering if applicable other
i
.t DC2-92-EM-N026 D8 l
September 17, 1992
'LVE SI-2-8923A FAILED STROKE TEST l
l l
MANAGEMENT
SUMMARY
On June 2, 1992, while performing current signature testing in accordance with work order C0096173 (ref. 1), valve SI 8923A would n(
ully open on the second and subsequent attempts to st.
<e the valve.
AR A0267535 (ref. 2) documents this testing.
Investigation revealed that the worm cartridge bearing locknut setscrew had not been adequately tightened.
This resulted in the locknut unscrewing itself from the worm shaft allowing the worm shaft to pull away from the spring pack.
This caused the torque switch to be pulled in the open direction.
With the torque switch open, the valve strokes until the torque bypass switch opens at about 35% of valve stem travel.
Operability Evaluation 92-12 (Attachment Three) addresses the functionality of the valves which may nave this.:
,,.,.,,..,_a condition.
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M 92NCRWPi92EMN026 JCN Page 1
of 18 Qg i
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i worm / spring-pack preassembly program for valve actuators not receiving an overhaul during 2R4-(ref. 4).
Valve SI-2-8805B also failed during post-l maintenance testing in 2R4.
.4 C.
Event
Description:
See Paragraph A.
above.
D.
Inoperable Structures, Components, or Systems that' l
92NCR%7.92EMN026)CN Page 2
of 18 l
l l
a,
l DC2-92-EM-N026 D8 September 17, 1992 Contributed to the Event:
None.
E.
Dates and Approximate Times for Major Occurrences:
1 1.
. June 2, 1992:
Discovery date.
During valve testing, valve SI-2-9823A would not fully open.
2.
June 12, 1992:
OE 92-12 presented to the PSRC and approved.
F.
Other Systems or Secondary Functions Affected:
None.
G.
Method ot Discovery:
On June 2, 1992, while performing current signature _ testing in accordance with work order C0096173 (ref. 1), valve SI-2-8923A would not fully open on the second and subsequent attempts to stroke the valve.
AR A0267535 (ref. 2) documents this testing.
H.
Operator Actions:
None required.
I.
Safety System Responses:
None required.
III.
Cause of the Event A.
Immediate Cause:
Investigation revealed _that the worm cartridge l
bearing locknut and setscrew had not been adequately tightened.
This resulted in the-locknut unscrewing itself from the worm shaft and allowing the worm shaft to-pull away from the spring pack.
This caused the torque switch to be pulled in the open direction.
With the torque switch open, the valve strokes until the torque l
bypass switch opens at about 35% of valve stem I
travel.
92NCRw792EMN026JCN Page 3
of 18 l
l l
l
+
DC2-92-EM-N026 D8 September 17, 1992 B.
Determination of Cause:
1.
Human Factors:
a.
Communications:
N/A.
b.
Procedures: There was no procedural guidance for securing the worm assembly locknut.
c.
Training:
There was no specific guidance in the procedure, therefore, there was no specific training.
d.
Human Factors:
N/A.
e.
Management System:
N/A.
2.
Equipment / Material:
l a.
Material Degradation:
N/A.
I l
b.
Design: There was a material substitution at the manufacturer, c.
Installation:
Personnel error.
d.
Manufacturing:
N/A.
e.
Preventive Maintenance:
N/A.
f.
Testing:
N/A.
i l
g.
End-of-life failure:
N/A.
I j
C.
Root Cause:
l The root cause is personnel error during the j
assembly of the spring pack assembly.
The individual did not adequately secure the worm shaft locknut in place.
See Attachment Four,
" Root Cause Analysis."
D.
Contributory Cause(s):
l 1.
Procedures did not include adequate instructions for tightening the setscrew or 92NCRWM92EMN026.Jcn Page 4
of 18 l
i f
DC2-92-EM-N025-D8 September 17, 1992
)
I the worm shaft locknut.
l 2.
The vendor changed the material hardness of the worm shaft affecting the effectiveness of l
the setscrew in deforming: worm shaft. threads j
for securing the locknut..
IV.
Analysis of the Event 4
A.
Safety Analysis:-
j See10E.92-12 (Attachment Three).
1 B.
Reportability:
i
{
1.
Reviewed under QAP-15.B'and determined to be.
]
non-conforming ~in accordance-with Section 2.1.2.
1 2.
Reviewed under 10 CFR 50;72 and 10 CFR 50.73 j
per NUREG 1022 and determined to not be j
reportable.. Reference 4' describes-the safety 1 functions performed'by'the potentially-l affected valves and. confirms that no plant-
)
safety feature is adversely affected'by the-H
~
locknut on the worm gear shaftfof1the Limitorque operator l coming: loose.
As'a conservative actionLa. jumper has been placed~
on one each per Unit of the CS-1(2)-8994A/B valves to ensure'that a. premature-torque; switch activation.will not limitivalve1 opening.
if required by an accident condition..
The existing plant conditions are' acceptable-for continued plant operation as documentednin-Attachment Three.
This condition has been determined by:DCPP management.to be reportable as a voluntary.LER;.see LER 1-92-010.for-j additional information.
3.
This problem does not require:a 10 CFR'Part 21-
- report, 4.
.This problem has been reported _viaLan'INPO j
Nuclear Network entry.'
5.
Reviewed under'10,CFR:50.9 and;determi~ned to be not reportablefsince this event-does not' have a significant implication for public 92NCRWh92EMN026KN Page 5
of 18
DC2-92-EM-N026 D8 September 17, 1992 health and safety or common defense and security.
6.
Reviewed under the criteria of AP C-29 requiring the issue and approval of an OE and determined that an OE is required (Att. 3).
V.
Corrective Actions A.
Immediate Corrective Actions:
1.
SI-2-8923A spring pack was disassembled, worm bearing tightened, setscrew ~ tightened, the operator reassembled and tested.
2.
An action plan to inspect other valve operators was developed and issued (Att. 3).
B.
Investigative Actions:
1.
Ensure the evaluation performed per 101 A0267749, of valve flow at a 35% to 40% open position is sufficient for system operability and that required operating torque is within the capability of the operator motor.
RESPONSIBILITY: M. Davido COMPLETE NECS I&C Engineering (NCEI)
AR A0267734, AE # 01 2.
NMAC and Limitorque will be contacted to establish the proper method for securing the locknut to the worm gear shaft.
RESPONSIBILITY:
H.' Campbell COMPLETE Electrical Maintenance (PGMB)
AR A0267734, AE # 02 l
3.
NECS - Engineering to evaluate the adequacy of the current maintenance practice of staking j
the locknut onto the worm, gear shaft.
RESPONSIBILITY:
L.
Pulley COMPLETE NECS I&C (NCEI)
AR A0267734, AE # 07
{
4.
Review NPRDS information for Limitorque valve operators to determine'if this problem has 92NCRW797EMN026JCN Page 6
of 18 l
I DC2-92-EM-N026 D8 September 17, 1992 been reported.
RESPONSIBILITY:
D.
Helete COMPLETE Reliability Engineering (PTRE)
AR A0267734, AE # 08 5.
Determine other Limitorque valve operator pre-assemblies, SMB-0, 00 and 000, that were-worked on by the same individual that l
performed work on the failed valve.
l RESPONSIBILITY: M.
Frauenheim COMPLETE Electrical Maintenance (PGMB)
AR A0267734, AE # 10 l
C.
Corrective Actions to Provent Recurrence:
l l
1.
An INPO Nuclear Network entry w.ll be drafted to convey the lessons learned from this event following determination of a root cause and corrective actions.
l RESPONSIBILITY: H.
Phillips COMPLETE l
Electrical Maintenance (PGEM)
AR A0267734, AE # 03 l
No OE required.
l Not outage related.
l Not an NRO commitment.
Not a CMD commitment.
2.
An INPO Nuclear Network entry will be posted for operating experience.
RESPONSIBILI?JY: J.
Nolan COMPLETE Regulatory Compliance (PTRC)
AR A0267734, AE # 04 No OE required.
Not outage related.
I Not an NRC commitment.
Not a CMD commitment.
3.
Review Limitorque maintenance procedures to' establish guidance for worm shaft locknut and setscrew installation.
RESPONSIBILITY:
F.
Amato COMPLETE i
Electrical Maintenance (PGMB)
AR A0267734, AE # 09 92NCRW792EMN026)CN Page 7
of 18
i e
DC2-92-EM-N026 D8 1
September 17, 1992 No OE required.
Not outage related.
Not an NRC commitment.
Not a CMD commitment.
4.
Tailboard the limitorque crews on the critical safety importance of limitorque operators and to attention to detail on all aspects of limitorque valves.
Additionally, cover the changes to E R'.10 I.J,K as well as the basis for these changes.
RESPONSIBILITY:
H.
Phillips ECD: 9/15/92 Electrical Maintenance (PGMB)
AR A0267734, AE # 12 OE required?
NO outage related?
NO NRC commitment?
NO CMD commitment?
NO 5.
Inspect Unit 2 valves - 8974A, 8974B, 8992, 89948 for loose locknuts or set screws.
RESPONSIBILITY:
H.
Phillips ECD: 5/31/93 Electrical Maintenance (PGMB)
AR A0267734, AE # 13 OE required?
NO outage related?
NO l
NRC commitment?
NO CMD commitment?
NO 6.
Track work activities for the removal and inspection of the spring pack from valve CS 8994A during 1R5 as docurented in AR A0267749, AE # 18.
RESPONSIBILITY:
R.
Hanson ECD: 11/30/92 Electrical Maintenance (PGMB)
AR A0267734, AE # 14 OE required?
NO outage related?
1R5 NRC commitment?
NO CMD commitment?
NO 7.
Procedure MP E-53.10J (SMB-00 Overhaul / Repair) will be revised to include specific instructions to inspect the locknut for correct tightness during each disassembly.
92NCR%7.92EMN026JCN Page 8
of 18
l DC2-92-EM-N026 D8 September 17, 1992 i
RESPONSIBILITY:
M. Frauenheim COMPLETE Electrical Maintenance (PGMB)
Tracking AR: A0273444 OE required?
NO Outage related?
NO NRC commitment?
NO CMD commitment?
NO i
l 8.
Provide a work activity to inspect the spring pack / worm assembly from SI-1-8821A, SI-1-8821B and RHR-1-FCV-641B.Just prior to the next regularly scheduled STP.
RESPONSIBILITY: R.'Hanson ECD: 11/5/92 Electrical Maintenance (PGMB)
Tracking AR: A0267749, AE # 15 OE required?
NO Outage related?
NO NRC commitment?. NO CMD commitment?
NO 9.
Provide a work activity to inspect the. spring pack / worm assembly from SI-2-8821A and SI 8823B just prior to the next regularly j
scheduled STP.
i l
RESPONSIBILITY: R.
Hanson ECD: 11/5/92 Electrical Maintenance (PGMB)
Tracking AR: A0267749, AE # 16 i
OE required?
NO i
Outage related?
NO NRC commitment?
NO CMD commitment?
NO D.
Prudent Actions (not required for NCR closure):
i 1.
Review the design of Limitorque operators to l
identify the critical' areas where material j
changes might potentially impact maintenance practices and analyze each for adequate controls.
Coordinate with NECS.
The ECD is intended for identifying the magnitude of the work required and not its completion.
RESPONSIBILITY: H. Phillips ECD: 1/31/93 DEPARTMENT: Electrical Maintenance Tracking AR: A0271835 l
92NCRW7.92EMN026)CN Page 9
of 18
.1
.DC2-92-EM-N026 D8 September 17, 1992 2.
Maintenance is making up special tooling to be able to grasp the wormcbetter to enable tightening of the worm gear locknut.
RESPONSIBILITY: R. Hanson-COMPLETE DEPARTMENT: Electrical Maintenance (PCMB)-
Tracking AR: A0272255 3.
Inspect all remaining.non-vitalLUnit 1/ Unit 2 SMB-00-Limitorque val /e operators within the next five years.
RESPONSIBILITY: R..Hanson ECD: 9/1/97 DEPARTMENT: Electrical Maintenance (PGMB)
Tracking AR: A0275083 VI.
Additional'Information A.
Failed Components:
Valve SI-2-8923A, suction isolation for SI: pump 2-1, FEG: 2 09 PIP, ID: 2 09 P VOM.SI-2-8923A.
B.
Previous Similar Events:
See reference 3.
C.
Operating Experience Review:
1.
NPRDS:
while p'rforming a speciali On August 8,.1985, e
inspection and test on the steam generator 1-1 main feedwater.stop valve, it was discovered that the valve would not " torque out".in the' open direction.
It was noted.that the spring pack did'not move at all.when the valve ~was tested.
A' damaged worm gear' shaft bearing locknut was discovered.
In this event _a SMB-4'Limitorque operator' failed to. torque out in the open direction _duer to a loose locknut on the. worm gear shaft.
l This event is not directly applicable'to DCPP because'in all'Limitorque-applications at DCPP.
the operators limit in the open' direction..
The open torque switch lprovides only'a backup u
function.
Referfto OE 92-12 (Attachment 3)'
92NCRWP\\92E.MN026.JCN
.Page-- 10. of.18 H
J
. ~ -
.=
l l
V DC2-92-EM-N026 D8 September 17, 1992-for Limitorque size O through 3~for further discussion.
2.
NRC Information Notices, Bulletins,: Generic Letters:
(
IEN 84-36, " Loosening.of. Locking Nut on Limitorque Operator" In>this event loosening offthe worm' shaft locknut on:a SMB-4 Limitorque I
operator permitted the torque switch:
from. stopping the motor:in the close
' direction ~after the valve >had fully closed.
In.this; application the.
operator contained'a unique:. feature 4
H that is.not found in most other valve i
applications in that these' units use a l
ball screw valve stem instead of a.
conventional acmelthreaded' valve stem.
The ball screw has the opposite hand (right-hand),. thread /to the standard' acme (lef t-hand) ' thread. - ;This-event-i is not directly applicable to DCPP because in all=Limitorque applications at DCPP utilize a standard acme-thread.
f l
3.
l None.
D.
Trend Code:
1.
Root Cause: EM (Electrical Maintenance)-A6
.(Other).
2.
Contributory'Cause: a.
EM-B2 (procedure i
deficiency', procedure incomplete).
b.
XXJ(Manufacturerf/
)
. supplier)-C1 (Material 1
deficiency,: design).
E.
Corrective Action Tracking:
The tracking action request-is A0267734.
1
~
i l
l
[
9mcawe.ntunonacu Page.11 of '18 i
., _ _... _, _ _ _. _. - _ _, _ =... _....,, _ -... _ ~,......,,.. -. - - -.....
i I
e DC2-92-EM-N026 D8 September 17, 1992 F.
Footnotes and Special Comments:
I See Summary of Craft Interviews, (Attachment Six).
G.
References:
l 1.
W/O C0096173.
2.
Initiating Action Request A0267535.
l 3.
4.
H.
TRG Meeting Minutes:
1.
On June 9, 1992, at 3:00 pm PDT in room 302 of the administration building, the initial meeting of the TRG convened.
A discussion of the background for this event, as noted above and in the references, was held.
Initial investigative and corrective actions were identified as noted above.
This TRG will reconvene on Tuesday, June 16, 1992 to discuss root cause of this event.
2.
On June 16, 1992, at 2:00 pm PDT in room 527' of the administration building, the TRG reconvened to discuss the status of investigative actions to date.
A preliminary determination has1been identified that personnel error may not have been a factor in this' event.
The hardness of the worm gear shaft of valve SI-2-892aA was checked and found to be significant greater than similar worm gear shafts in other similar Limitorque valve operators.
A review of the hardness of replacement worm gear shafts in warehouse stock showed some much harder than others.
Additional investigation into the hardness of worm gear shafts previously replaced in installed Limitorque valve l
operators will be completed by the next TRG reconvene.
l l
92NCRWP.92EMN026]CN Page 12 of 18 6
1 i
i DC2-92-EM-N026 DB i
September 17, 1992 Additional investigative actions, as noted above, were identified by the TRG.
Vendor contact for additional information has not been completely successful to date; this action will continue to be pursued.
l l
l The TRG will reconvene on Tuesday, June 23,.
1992 to discuss progress of investigative I
actions.
3.
On June 23, 1992, at~1:00 pm PDT in room 527 l
of the administration building the TRG 1
reconvened to discuss the progress of investigations into the root cause and scope i
of worm gear _ shaft locknut loosening.
Potential root causes discussed include a i
variation in the material or hardening.rocess for the worm-gear shaft indicated by the variable results of' hardness testing of the valve operators in the plant and warehouse.
An additional root cause, or'possibly a i
contributing cause, is the lack of any
{
technical guidance from the vendor or other H
sources on the installation technique for the worm gear shaft locknut setscrew.
Tentatively, the harder worm gear shafts are associated with two purchase orders for 26 Unit i valves and 16 Unit 2 valves.
Additional investigation continues.
A reportability determination will be expeditiously made (as documented above).
Additional consideration will be given to a
" common mode failure" type event and/or a 10 CFR Part 21 report as additional information is collected.
The OE will be revised to include all valves in the plant that have Limitorque model SMB-00 and SMB-000 operators.
The TRG will reconvene on Wednesday, July 1, 1992 to evaluate the event _information collected to that time.
4.
On July 1, 1992, at 1:00 pm PDT, in room 533 92ncawr92tuno26.Jen Page 13 of 18
9 i).'
DC2-92-EM-N026 D8 September 17, 1992 l
of the administration building, the TRG reconvened to review investigations to date.
Plans are being considered to inspect every
(
Limitorque SMB-00 operator that has not yet been inspected during the next refueling outages.
A telephone conversation between PG&E and l
Limitorque established that the worm shaft material has been changed and Limitorque currently supplies worm shafts on either material interchangeably.
Shop tests have shown that if the worm shaft locknut is " finger-tight," the nut can unscrew several turns when the operator motor is started.
OE 92-12 (ref. 5) does not address Limitorque operators worked during 1R4 and 2R4 that did not have worm shaft /gcar replacement but may have had the worm shaft locknut loosened during maintenance.
Maintenance is considering the development of another list of Limitorque operators to be inspected based or this criterion.
Inspection of 28 Limitorque_ valve operators-that were worked by individuals other than the one who worked the failed valve did not identify any loose locknuts.
Five of the 11 worked >by the individual who worked the failed valve had loose locknuts.
Electrical Maintenance (R. Hanson) to provide a root cause statement with. illustrations.
Documentation of personnel-statements will be included in the NCR writeup by Electrical Maintenance (R. Hanson).
The TRG will reconvene on or about July 22, 1992 to discuss the results of inspections and investigations.
5.
On July 22, 1992, at 1:00 pm PDT in room 533 of the administration building, the TRG 92NCRMB92EMN026JCN Page 14 of 18 e.m,,,-
m
I i
DC2-92-EM-N026 D8 September 17, 1992 reconvened to review the root cause analysis.
A cause analysis was reviewed and the root cause was determined to be personnel error on the part of the craftsman.
Only the Limitorque valves serviced by this individual experienced any problems.
Contributory causes l
looked at were the variation of material hardness in the worm bearing cartridges and the lack of procedural guidance for installing the locknut and setscrew (no. torque values for the locknut.)
Review of every Limitorque was determined as unnecessary in light of the root cause and the possibility of causing more problems than it would solve.
Only the remaining unchecked valves that were serviced by the individual will be looked at (Unit 2 8971A, 8974B, 8992A, 8994B.)
l The following corrective' actions were identified:
a.
Revise. procedure E-53.10 I,J,K to provide adequate details for worm bearing assembly. Specifically the locknut and set screw. Tailboard the Limitorque crews on the critical safety importance of Limitorque operators and to attention to detail on all aspects of Limitorque valves.
b.
Inspect Unit 2 valves - 8974A, 8974B, 8992, 8994B for loose locknuts or set screws.
The following prudent action was' identified:
Review the design of Limitorque operators to identify the critical areas where material changes might potentially impact maintenance practices and analyze each for adequate controls coordination with NECS.
The TRG agreed to reconvene on 8/7/92 at 1:00 pm to discuss Unit 1 outage replacement.
6.
On August 7, 1992, the TRG reconvened in room 533 of the administration building at 1:00 pm l
92NCRWP\\92EMN026JCN Page 15 of 18
,e DC2-92-EM-N026 D8 September 17, 1992 l
PDT to discuss what further valve inspections are required and whether they will be.
corrective ~or prudent.actionsffor this NCR.
Inspections to date have been performed on three groups of valves; 1) the valves that:had pre-assembled spring packs on:Unitr21(the-only-population of valves that have had locknut problems), 2) a group.of' valves'from Unit:1 that had pre-assembled. spring-packsfand~3) a group of spring packs.that had been removed as original equipment from valve operators which had been in service.
The results.of these inspections 1are-summarized in Attachment'Five.
AR A0269028 addresses the need forfa.QE'not being issued for the failure 1of MOV SI
- 8305B.
This AR was briefly discussed during the meeting and was. deferred until the next reconvene of this TRG.
Regulatory Compliance willireview OE 92-12 to ensure corrective actions correlate with those included in this NCR, making revisions to the.
NCR as necessary.
This TRG will reconvene on AugustL25, 1992'to.
review the NCR writeup.for, accuracy-prior to presentation to the PSRC.
7.
On August 25, 1992, the'TRG-reconvened in room 527 of the administration buildingJat'1:00'pm
-l PDT to review the current NCR:writeup for~
~
]
accuracy.
l An additional-AE was requested:to track the.
1 I
TRG Chairman's. review of the.voluntari LER l
reporting the: subject of this.NCR to ensure.
l any commitments made'in the LER were I
consistent with and do: not exceed those actions identified in this NCR.- ;The target-date for this LER submittal.is September 17L 1992.'
The TRG will reconvene for-signoffiofLthe.NCR l
prior to-placing-it onto the'PSRC agenda on September 2, 1992 at 10:00 am PDT.
92Ncawrw2rxNo26;cu Page 16 of 18 1
1 I.
9 DC2-92-EM-N026 D8 September 17, 1992 8.
On September 2, 1992, the TRG reconvened in room 424 of the administration building at 10:30 am PDT with the intent of signing the NCR prior to presentation to the PSRC.
Numerous minor' revisions were identified aus being desirable to include in the:NCR writeup before presentation'to the PSRC.
It was agreed that Regulatory Compliance would incorporate the revisions and Email the ASCII file to those who would sign.the NCR for their review prior to circulating the NCR for signature.
AR A269028269028was discussed by the TRG and
{
determined to be outside the scope of this NCR.
This NCR was issued in a timely manner following the first repeat failure of e..d MOV to pass its STP (8923A).
The previous valve failure (8805B) had no previous failure history and was correctly considered as an isolated incident.
This NCR will be walked in for presentation to the PSRC or added to the PSRC agenda for the September 28, 1992 meeting.
I.
Remarks:
In a phone call between PG&E and.the NRC on June 23, 1992, beginning at 10:00 am PDT, the following facts were established:
1.
There is an interference fit between the worm gear shaft and the caged bearing ID that can.
act to transmit torsional inertial forces contributing to the loosening of the worm gear l
shaft locknut.
2.
There were a number of valve stroke cycles (more than 10) necessary to produce the loosening of the worm gear shaft locknut in valve SI-2-8923A, i.e., there was no sudden or instantaneous loosening of the locknut on the shaft during a single valve stroke.
J.
Attachment (s):
92Neuwn9;Exso2eacN Page 17 of 18 i
DC2-92-EM-N026 D8 September 17, 1992 1.
Worm and Bearing Cartridge Assembly Exploded View.
2.
MOV Status as of June 23, 1992.
3.
OE 92-12.
4.
Root Cause Analysis.
5.
BREAKDOWN OF LIMITORQ'.TE NUMBERS OF OPERATORS (BY SIZE) AT DCPP.
f 6.
Summary of Interviews With Craftsmen.
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92Ncawn92twNo26 >cN Page 18 of 18 l